What we talk about when we talk about lice: Lice story, Part II


So can a big one, if it's a body louse and not a head louse.

There are few very important things to know about lice.

First of all, lice are very species specific. Cattle lice (there are 4 common kinds in the United States) do not infect sheep. Sheep lice do not infect hogs. And what ever Rick Santorum’s current anxieties are, no species of animal lice infects people. I am sure that he will sleep better knowing this.

Secondly, lice are often quite specific to an area of the body. Human head lice (Pediculis capitis humanus) stay on the head. They do not like moving towards the torso. They like to lay their eggs on hair.

Picture from Wikimedia Commons

Body lice–Pediculus humanus humanus, or sometimes Pediculus humanis corporis–are indistinguishable from head lice, yet except in the laboratory, they will not breed with head lice. They prefer to lay eggs in clothing, especially along the seams. (Bad infestations, therefore, can be prevented by avoiding clothing.)

Thirdly, there is an  important distinction between head lice and body lice from an epidemiological point of view. Head lice really don’t cause any serious problems. Kids get sent home from school, squeamish parents lose it and stay up all night itching–even though they are not infested–and the washing machine and vacuum cleaner do overtime. However, other than the chaos and the irrational panic, there is little to worry about.

Body lice, on the other hand, are the vector for some rather serious diseases.

Epidemic typhus

Spread in the feces of lice (like Chagas’ Disease), epidemic typhus is caused by infection with the bacteria Rickettsia prowazekii. Typhus is one of the reasons that, at least until our last couple of wars, more death to soldiers and civilians during conflicts has been caused  by germs and disease than by bullets, cannonballs, spears, arrows, bayonets, bombs…..

Trench Fever

Caused by the bacteria Bartonella quintana, trench fever is described as a “moderately serious” disease, and though rarely lethal, was responsible for yet another of the epidemics that plagued soldiers during the War to End All Wars. It is not to be confused with Trench Mouth or Trench Foot, both of which also plagued soldiers in the First World War.

Louse-Borne Relapsing Fever

Caused by Borrelia recurrentis, relapsing fever occurs epidemically in areas of poverty and deprivation. It is currently prevalent in Sudan. If left untreated, mortality rates can reach 30%-70%

Take home message: Head lice don’t cause disease, and war, poverty, and deprivation are bad for your health.

Keep Smiling!


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